The charging system of a telecommunications system is by many considered to be one of the most important parts of the telecommunications system. Certainly the operator is interested in a charging system that actually charges clients for used services. A client of an operator is especially interested in that the charging is fair so that he or she is not being charged for any services that he or she has not used or received. Fair charging is also important to the operator from a business perspective. An operator that is known for unfair charging will have trouble selling its services, while an operator who is able to offer a more flexible charging that is adjusted to the type and quality of service that a client actually receives is given a competitive edge.
The basis of charging differs between different types of services. For some types of services the charging is based on volume, e.g. amount of delivered data bits and for other services on time, e.g. the duration of a communications session. There are also services that are charged per usage of the services, so-called service based charging. With service based charging volume charging may be turned off, e.g. for charging of MMS (Multimedia Messaging Service), where the operator may choose to charge per sent and delivered message instead of basing the charging on the number of sent and delivered data bits. Different types of charging may also be combined and applied differently depending on the user of the service.
Charging aspects in 3G systems are discussed in 3GPP TS 32.200 V5.5.0 (2003-09), 3GPP TS 32.015 V3.11.0 (2003-03) and 3GPP TS 12.15 V7.7.0 (2002-12).
The transfer of data over wireless links may give rise to charging problems not encountered when transferring data over fixed wired connections. The bandwidth that is available for a radio connection in a mobile communication network may vary very fast due to changes in the characteristics of the air-interface caused by e.g. shadowing, or due to redistribution of the assigned bandwidth to the users in a cell. In conventional systems this may lead to situations where an end-user pays for something he/she never got or to situations where the end-user pays an unreasonably high amount in relation to the delivered quality of service.
Consider for instance a packet switched PDP (Packet Data Protocol) context that is activated between a mobile phone and an application server. The activation of the PDP context will cause different nodes e.g., SGSN (Serving GPRS Support Node), GGSN (Gateway GPRS Support Node) and the application server, to generate Charging Data Records (CDRs). CDRs in SGSN and GGSN are based on volume, i.e. the amount of IP-packets that has been transported in the network. When the PDP context is up, the network transports IP-packets from the application server to the mobile phone. When these IP-packets are transported it could happen that the end-user temporarily is “out-of-connection” with the application server e.g., when the user moves indoor where the coverage is poor or when a cell re-selection occurs. Cell re-selection occurs e.g. when the end-user is moving from a WCDMA system to a GSM system (or vice versa). During cell re-selection there is a long IP-session interrupt.
If an interruption happens this might for some types of sessions trigger the end-user to terminate the session. However since there is no connection between the end-user and the application server for the time being, the application server is unaware that the end-user has terminated the session.
Thus the application server will continue to produce CDRs which leads to a situation where the end-user pays for something he/she never got.
Bandwidth changes and interrupts may also lead to a longer session and perceived bad service so that the client finds it unacceptable to pay the same amount for the session as he/she would for a session without as many bandwidth changes and interrupts.
Even if there is no complete interruption the available bandwidth on the wireless communications link to the mobile phone may decrease to such an extent that some IP-packets have to be discarded by the RNC (Radio Network Controller) and thus not delivered to the end-user. However other nodes may already have generated CDRs for the packets that later are discarded by the RNC so that the end-user ends up paying for packets that were never delivered to him/her.
From the above-described example it is clear that problems with unfair charging may arise during data bit transfer sessions involving wireless links in conventional telecommunications systems.